Today, many refrigeration systems are vapor compression based and utilize a thermostatically regulated duty cycle control. However, typical vapor compression based refrigeration systems are not dynamic enough to meet both steady state and transient demand, such as during pull down or recovery. Thus, vapor compression based refrigeration systems tend to have excess cooling capabilities that far exceed heat extraction demands required during steady state operation. While the extra capacity provided by the excess cooling capabilities allows improved pull down performance, large current surges prevalent during start-up require higher capacity and consequently more expensive components to handle the loads. Moreover, the large current surges and loads incurred by duty cycle control excessively wear the components, thereby potentially causing premature failure. Further, by the very nature of their control, thermodynamic limits, and product performance demands; vapor compression based refrigeration systems are less efficient than optimum.
The sub-optimum efficiency disadvantage of vapor compression based refrigeration systems relates to precisely controlling the temperature within a cooling chamber. Typically, when a temperature within a cooling chamber exceeds a certain value, the vapor compression based refrigeration system activates and continues to run until the temperature in the cooling chamber is below the certain value. Once the cooling chamber reaches a temperature below the certain value, the vapor compression based refrigeration system shuts off. Nonetheless, in addition to excessive wear as noted above, this type of control scheme will typically have a relatively large control band and a relatively large internal temperature stratification in an effort to minimize energy consumption and allow for operation in varied ambient conditions. This regime is most often utilized because throttling or capacity variation is difficult and expensive to implement into the vapor compression cycle and provides limited efficacy as volumetric efficiency falls.
Accordingly, systems and methods are needed for precisely controlling the temperature within a cooling chamber where the efficiency of the components used to extract heat from the cooling chamber is maximized. Also, systems and methods are needed for mitigating heat rejection limitations of the components used to extract heat from the cooling chamber.